Signal converter and amplifier for metering additive flow

ABSTRACT

An additive liquid is metered to a flowing liquid through an adjustable linear valve. A turbine meter provides a pulse train proportional to flow in the main line. A servo system includes a servomotor positioning the valve and a differential amplifier circuit to control the motor. The amplifier circuit includes a first channel connected to the turbine meter to convert the pulse train to a related D.C. analog signal which is connected across a ratio selection potentiometer. The amplifier circuit includes a second channel connected to the feedback potentiometer which is energized from a properly scaled D.C. source through a pressure compensating variable resistor to compensate for different main line pressures. A differential summing amplifier is connected to sum the two signals and establish a corresponding polarity signal for energizing a polarity sensitive relay which connects the servomotor to properly position the valve.

United grates @atent Krause et al.

[54] SIGNAL CONVERTER AND AMPLIFIER roe MErERmG AnnmvE FLOW [72]Inventors: Ronald O. Krause, Waukesha, Wis;

Kenneth J. Ayala, Winter Park, Fla.

[73] Assignee: Nutrico, Inc., Milwaukee, Wis.

[22] Filed: Feb. 26, 1971 [21] Appl. No.: 119,086

[52] US. Cl ..137/101.21 [51] int. C1 ..Fl6k 19/00 [58] Field ofSearch..137/101.19,101.21,114

[56] References Cited UNITED STATES PATENTS 3,038,486 6/1962 Thurman..137/101.21x

Primary ExaminerRobert G. Nilson Attorney-Andrus, Sceales, Starke &Sawall [15'] answer 5] Aug. 29, 1972 from a properly scaled D.C. sourcethrough a pressure compensating variable resistor .to compensate fordifferent main line pressures. A differential summing amplifier isconnected to sum the two signals and establish a corresponding polaritysignal for energizing a polarity sensitive relay which connects theservomotor to properly position the valve.

9Claims,2DrawinglFigures l W1 1| In Ill J SIGNAL I CONVERTER L a S AMPw: POINT PRESSURE i COMFENSATOR PATENTE flAuszs m2 INVENTORS O. KRAUSEKENNETH J. AYALA %4/W Attorneys BACKGROUND OF THE INVENTION Thisinvention relates to a control circuit for modulation of the amount ofmaterial added to a liquid flow and, in particular, in accordance withthe liquid flow rate.

In various processes, a small amount of a second material is desirablyadded to and blended with a relatively large and rapidly flowing liquidstream. For example, in the processing of various liquid foods such asfruit juices, beer, soft drinks and the like, liquid sterilizing agentshave recently been suggested as a substitute for the more traditionalheat-sterilization of the liquid during the processing. A particularlysatisfactory system and apparatus is shown in US. Pat. No. 3,506,460 toPeter D. Bayne. As more fully disclosed therein, a small amount of asparingly soluble sterilizing agent is introduced and blended with theflow stream of the liquid perishable material prior to the packagingthereof. An injector unit is mounted in the main stream flow line and isinterconnected through a valved line to a storage unit. In this manner,small amounts of the sterilizing agent are introduced into the flowingliquid. An in-line blender is preferably provided immediately followingthe injector unit to agitate the liquid and the sterilizing agent andinsure full dissolving of the sterilizing agent in the liquid. In orderto provide accurate control of the amount of the sterilizing agent, aflow sensing means is connected in the main flow line and produces asignal which is coupled through a suitable converter to control thesetting of a flow valve in the sterilizing agent flow line. The valve isshown as a motor-operated variety or the like which opens and closes inaccordance with the flow rate to maintain a predetermined flow.

Applicants have found that the flow rate may vary substantially andrapidly and that the apparatus presently employed in additive controlsdoes not produce a highly accurate proportion of additive material tothe liquid flow, particularly at extremely low ratios. Thus, as noted inthe above Bayne patent, in the sterilization of liquid food products andthe like, extremely low ratios of additive to base liquid flow areemployed. Typically, the sterilizing agent added to the perishablematerial is in the range of 0.000122 grams per liter. Although pumpingand batch loading have also been suggested, they are not sufficientlyaccurate where parts per million type injection rates on a continuingbasis are required such as in the application for sterilization of foodproducts.

An unusually satisfactory monitoring system is disclosed in theapplication of R. O. Krause, entitled Continuous Control For IntroducingMaterial Into A F lowing Liquid which was filed on Feb. 26, 1971 withSer. No. 119,087 and which is assigned to a common assignee with thisapplication. Generally, a flow-sensing turbine meter is connected in themain flow line and establishes a related train of pulse signals whichare fed to a suitable signal comparator and amplifying circuit means toestablish an operating control signal. The error signal is connected toa servomotor which, in turn, is connected to position a control valveand simultaneously to position a related feedback signal generator whichproduces a signal related to the valve position. The control valve, inturn, is selected as a linear positioning valve whereby each unit changein the position of the valve establishes a corresponding change in flowsuch that the position of the valve accurately determines the amount offlow. The output of the generator is connected into the amplifying meansand summated with the flow related signal and a set point signalestablished by a set point signal unit. The latter signal unitestablishes a signal corresponding to that of the flow sensing means andthe feedback generator when the desired ratio of the additive to theliquid flow is present. The circuit thus compares the three signalsconsisting of the set point signal, the flow-related signal and thefeedback signal to produce a closed loop drive of the valve servomotorwith a corresponding accurate positioning of the control valve.

SUMMARY OF THE INVENTION The present invention is particularly directedto a reliable and practical electrical servo control circuit including adifferential amplifying circuit providing a rapid response for precisemetering of the preselected relatively minute portions of the additivematerial to a flowing liquid on a continuous basis.

A flow meter is connected in the flow line and establishes a flowrelated signal such as the train of pulses from a turbine meter, inaccordance with the liquid flow. In accordance with the presentinvention, the signal is applied to the servo control circuit andparticularly to one of a pair of signal channels for connecting theseveral electrical control signals to the input means of a differentialamplifier. A set point signal means establishes an appropriately scaledset point signal related to desired proportion of additive material tothe flowing liquid. A pressure compensating signal means produces acorrespondingly scaled signal which compensates for the back pressure ofthe process flow line and which will affect the interrelationshipbetween the set point signal and the flow-related signal. In one aspectof the invention, the flow-related analog is connected to energize apreset selection potentiometer having an output tap connected to theinput of the differential amplifier. The output of the differentialamplifier is thus an analog signal related to the comparison of the setpoint setting of the potentiometer and the flowrelated signal. This isconnected to and drives the servomotor to correspondingly position thecontrol valve and a linear precision feedback signal means such as apotentiometer. The feedback signal is a related analog signal which isfed back to one of the channels to appropriately modify the signal andto maintain accurate drive and position of the servomotor until theflow-related signal as modified by the set point setting just balancesthe feedback signal. Applicants have found that this circuit provides arapid and accurate response required to produce optimum metering of therelatively small amounts of an additive to continuous flowing liquid.

In a preferred and novel construction of the present invention,- the twochannels to the differential amplifier include a first channel connectedto the output of the turbine meter. This first channel includes adigital to analog converter to establish an alternating current signalproportional to the pulse rate of the output of the turbine meter. Adetecting and rectifying means is coupled to the converter andestablishes a corresponding direct current analog signal. The analogsignal is further amplified and connected across a selectionpotentiometer having a tap to permit selection of a portion of theflow-related signal. The potentiometer tap is manually set to thedesired additive rate and is coupled through an amplifier to a linearsumming resistor connected to the input of a summing amplifier. Thesecond signal channel includes a feedback potentiometer having a tapcoupled to and driven by the valve positioning servomotor. The tap ofthe feedback potentiometer is also coupled by an amplifier to a linearsumming resistor to the same input of the summing amplifier. The outputof the summing amplifier is a polarity relatedsignal corresponding towhichever signal is greatest. This signal is applied to a polaritysensitive relay having forward drive contacts and reverse drivecontacts. The servomotor is a precision reversible motor having aforward drive circuit and a reverse drive circuit means. The forwarddrive circuit means is connected to power through the forward drivecontacts of the polarity sensitivity relay and the reverse drive circuitmeans is similarly connected to power by the drive contacts of therelay. The servo motor is thereby driven to position the valve and theinterconnected potentiometer to establish a null output from the summingamplifier.

The summing amplifier is preferably provided with a feedback networkincluding a variable resistance means to permit adjustment of thecircuit sensitivity and a stabilizing capacitive response network.

The present invention provides a high satisfactory controi circuit whichestablishes a sensitive and rapid response for positioning of the linearmetering valve and thus is particularly adapted for monitoring theaddition of relatively minute quantities of an additive to a flowingliquid of a perishable material in a continuous manner and in responseto rapidly varying rates of flow.

BREEF DESCRIPTION OF THE DRAWING The drawing furnished herewithillustrates the best mode presently contemplated for carrying out thesubject invention and clearly discloses the above advantages andfeatures as well as others which will be readily understood from thefollowing description.

In the drawing:

FIG. 1 is a block flow and control diagram showing the invention appliedto the addition of a liquid sterlizin g agent to a main flowing liquidproduct; and

FIG. 2 is a schematic circuit diagram of the signal converter andamplifier circuit shown in FIG. 1 constructed in accordance with theteaching of the present invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring to the drawings andparticularly to FIG. 1, a main liquid flow line 1 is shown for carryinga perishable liquid such as beer, fruit juice, soft drinks, wine or thelike from a source 2 to any suitable further processing means, notshown. A sterilizing agent additive line 3 is connected to the line ithrough an injection unit 4 to supply small amounts of a liquidsterilizinn agent from a pressurized additive source 5 to the liquidflowing through line 1. A control valve 6 controls the amount of liquidadditive supplied to unit 4. The

liquid sterilizing agent may, for example, be a diethyl pyrocarbonate ormixed anhydrides or the like which when dissolved in the perishableliquid, eliminates the necessity for the usual subsequent heatsterilization. Generally, in accordance with the present invention, aflow meter 7 is connected to the line 1 immediately downstream of theinjector unit 4 and establishes an electrical output signal which isapplied via a line 8 to a signal converting and amplifying circuit 9. Aset point signal generator 10 establishes an electrical signal scaled tothe signal output of the meter and is connected to a second input line11 to the circuit 9.

A pressure compensator 12 is also connected to the signal converter andamplifier 9 to compensate for the pressure in the main flow system andparticularly line 1.

The sterilizing agent within the source or tank 5 is maintained under apredetermined constant pressure, such as from a fluid pressure supplymeans 13. The valve 6 is a linear valve unit such that the flow of thesterilizing agent through the additive line 3 is precisely related tothe constant pressure, the sized opening of the valve 6, and the backpressure of line 1.

The preset and flow related signals are compared and generate adifference signal at an output line 14 which, in turn, is interconnectedto drive a servomotor assembly 15 for positioning of valve 6. Generally,assembly 15 includes a servomotor 16 coupled to control the position ofthe additive valve 6 and also coupled to correspondingly position afeedback potentiometer E7. The control valve 6 is a suitable linear-typevalve such as a spring-loaded variable orifice valve which will permitaccurate metering in accordance with the opening of the valve, generallyas more fully disclosed in the copending application of R. O. Krauseentitled Continuous Control For Introducing Material Into A FlowingLiquid" which was filed on the same day as this application and isassigned to the same assignee. The motor 16 thus opens and closes thevalve 6 to vary the additive flow from the source 5 to the injector unit4 to thereby adjust the quantity or amount of the sterilizing agent fedto the main line i.

The motor 16 simultaneously positions the feedback potentiometer 17 toestablish an analog signal directly related to the opening of the valve6 as determined by the position of the servomotor 16. The potentiometeroutput signal is also connected via a line 18 to the converter andamplifying circuit 9 and summated with the difference signal toestablish an error signal equal to the difference between the sensederror and the error in the setting of the valve 6 and thereby createprecise movement of the servomotor i6 and a corresponding positioning ofthe control valve 6 until the error signal is effectively zero.

A suitable blender 19 is connected in the main flow line i and ispreferably a suitable static blender to fully mix the additive and themain liquid.

A cutoff valve 29 is shown inserted in the additive flow line 3 betweenthe control valve 6 and the injection unit 4. The valve 20 may be asolenoid-actuated valve or the like interconnected to the signalconverter and amplifying circuit 9. If the output of the meter 7 dropsto indicate a predetermined minimum flow rate in the main flow line 1,the valve 3 is actuated to close the additive flow line and terminatethe flow therethrough.

Thus, in the operation of the illustrated system, the operator sets theset point generator and the pressure compensator 12 in accordance withthe particular characteristics of the flow line and the desired additiverate. The modified preset signal is compared to the output of theturbine meter 7 and provides a drive for the opening of the linearcontrol valve 6 in accordance with the preset amount. In addition, aninner control loop is provided by the feedback potentiometer 17 toinsure accurate positioning of the servomotor in accordance with theerror signal. The linear control valve 6 provides a very precisemetering while the feedback system is based on the valve position ratherthan any special sensing of the actual additive flor rate. This isparticularly desirable and provides a more accurate control than wasobtained by determination of the small amount of flow of the additivematerial. If the main liquid flow should drop below a predeterminedlevel, the output actuates the cutoff valve 20 to terminate the additiveflow.

As more fully disclosed in the previously referred to Bayne Pat. No.3,506,460, the sterilizing agent tank 5 is preferably maintained at .apressure of at least five pounds per square inch and preferably in therange of 25 to 35 pounds per square inch above the pressure of thebeverage in line 1. The storage tank 5 is preferably pressurized by aninert gas such as nitrogen which is introduced into the storage tank orthe head space of the tank from a suitable pressure source which ispreferably a regulated pressure source to maintain the desired pressureconditions in the storage tank and therefore on the additive in the flowline.

A highly satisfactory pin type control valve 6 which has been employedis a micro-metering valve 22RS4 sold by Whitey Research Tool Co. ofErneryville, Cal, as shown in the previously identified copendingapplication, entitled Signal Converter and Amplifier for MeteringAdditive Flow.

Referring particularly to P16. 2, the signal converter and amplifyingcircuit 9 is constructed in accordance with the teaching of the presentinvention and includes a pickup channel 46 for converting the output ofthe turbine meter 7 into a related analog signal, which is connected toenergize the set point generator 10 and applied to one side of acomparator channel 47. The opposite side of the comparator channel 47 isconnected to the feedback potentiometer 17 which is connected in circuitwith a suitable pressure and calibration adjustment means.

More particularly, as shown in E6. 2, the turbine meter 7 includes apickup coil 48 associated with a magnet core 49. The rotor 50 of theturbine meter 7 includes a rotating magnetic control device 51 such thatthe rotation of the unit generates one or more pulse signals in the coil48 for each revolution. Thus, the output of the turbine meter 7 appearsat the coil 48 as a series of time-spaced induced voltage signalsrelated direct y to the rotational rate of the turbine meter rotor,which, in turn, is directly related to the volumetric flow. The outputof the coil 48 is connected through a resistive coupling network 52 tothe input of an amplifier 53 having its output capacitive coupled to theprimary of a detector transformer 54. A pair of diode rectifiers 55 areconnected to the opposite ends of the secondary winding 56 oftransformer 54 and are similarly polarized with respect to a commonoutput terminal 57 to establish a fullwave rectified voltage withrespect to a grounded center tap connection 58. The fullwave outputprovides a related direct current signal connected through a couplingresistor 59 to the inverting input of an operational amplifier 60. Astabilizing feedback potentiometer 60a interconnects the output of theamplifier 60 to the input to establish an operational amplifyingnetwork, the output of which is a direct current signal proportional tothe flow rate. A resistor and a bypass filtering capacitor 61 to groundconnects the output to the non-inverting input of a second operationalamplifier 62, the other input being interconnected through a feedbackline 63 to the output. The resistor-capacitor 61 will filter spurioustransient signals and the like from theoutput stage and thus result indriving of the amplifier 62 in accordance with the converted analogflow-related signal.

The output signal is applied across a proportioning potentiometer 64connected between the output of the amplifier and ground. Thepotentiometer 64 includes a tap 65, connected as an input to channel 47through a manually operated test switch 66. The setting of thepotentiometer 64 determined the proportion of the flow-related voltageemployed as an input to actuate the servo system and thereby permitsadjustment of the amount of additive for any given flow in accordancewith a desired range. Generally, the potentiometer 64 is a precisionlinear potentiometer which may be calibrated in parts per million topermit direct settingof the additive in parts per million for any givenflow rate.

The output tap 65 of the potentiometer is coupled at one input to thenon-inverting input of an operational amplifier 67 of channel 47 with afurther stabilizing capacitor 68 connecting the potentiometer tape 65 toground. The output of the amplifier 67 is connected on one input of aservo-drive amplifier 69 by a precision resistor 70, the output of whichis connected to control the energization of the servomotor 16 aspresently described.

Amplifier 69 is an operation amplifier having a suitableresistor-capacitor feedback network 71 connected to the inverting inputof amplifier 69.

A feedback amplifier 72 similar to the flow-related signal amplifier 67has a corresponding non-inverting input connected to the tap 73 of theservo-driven potentiometer l7. Tap 73 is coupled to and positioned bythe servomotor 16 to establish a signal proportional to the opening ofvalve 6. The one side of the potentiometer 17 is grounded and theopposite side is connected in series with a pressure adjustmentpotentiometer 74 and a calibrating potentiometer 75 to the positive sideof a DC. power supply. A span adjustment potentiometer 76 is shownconnected in parallel with the pressure adjusting potentiometer 74.

In the operation of the circuit, the input to the feedbackservo-position related amplifier 72 establishes an output in accordancewith the position of the servomotor l6 and therefore the additivecontrol valve 6. The output of the amplifier 72 is coupled through aprecision resistor 77 to the summing input of the servo-drive amplifier69 in common with the output of the flow-related drive amplifier 67. Theopposite inputof the amplifier 69 is grounded through a precisionresistor 78. The operational amplifier includes the feedback network 731which has a potentiometer 79 in series with a fixed resistor 80interconnecting the output of the amplifier to the summing input. Asmall filtering and shaping capacitor 81 is connected in parallel withthe fixed resistor 8%. The output of the amplifier 69 is apolarityrelated DC. signal directly proportional to the algebraicsummation of the output of the feedback amplifier 72 and theflow-related amplifier 67. The output of the amplifier 69 is connectedto energize a polarity sensitive relay 82.

The relay 82 is shown schematically as a single pole, double-throw unithaving a common pole $3 connected to one side of an alternating currentpower supply and selectively engaging a forward drive contact 84 andreverse drive contact 85. The contacts 84 and 85 are connected toselective energize the servomotor 16, the opposite side of which isconnected to the opposite side of the alternating current power supply.

The servomotor 16 is shown as a conventional servomotor having a pair ofwindings 86 and 87 connected in common at one end to the alternatingcurrent power supply line. The opposite ends of the windings 86 and 87are connected directly to the forward drive contact 84 and the reversedrive contact 85 respectively. A resistor 3% in series with a capacitor89 is connected across the contact connection to the two windings 86 and87. Thus, with the relay common pole 83 connected to the forward drivecontact 84, the forward drive winding 86 is connected directly acrossthe AC. power line while the winding a7 is connected across such linesin series with the resistor 88 and capacitor 89. Conversely, when thecommon pole 83 is connected with the reverse drive contact 85, thereverse driving winding 87 is connected directly across the power linesand the opposite winding $6 is connected across the power lines inseries with the resistor 88 and the capacitor 89. This provides for theopposite rotation of the servomotor and a corresponding rotationpositioning of the valve shaft 43 and the tap of potentiometer 17, asdiagrammatically shown by the opposite extension of the motor shaft.

in the illustrated embodiment of the invention, the several componentsof the circuit may be tested through the opening of the test switch 66and the selective connection of a DC. power test supply directly intothe circuit at appropriate points through a manually operated switch 90.Thus, in the illustrated embodiment of the invention, a DC. test supplyis provided via the common pole 95 of the switch 90 having a pluralityof contacts, a first contact 92 is connected directly to the flowrelated input line to the differential amplifier network. This permitsinsertion of a preset flow simulated signal. A second contact 93provides a corresponding input to the servo input line to theoperational amplifier 72 directly to simulate the output of the feedbackpotentiometer E7. The third contact 94 permits corresponding DC. inputto the input supply connection of the series parallel potentiometers 7376 to energize amplifier 72 through the several calibration andadjustment potentiometers. A fourth contact 95 provides an input signalof the DC. power supply connection. Fifth and sixth contacts 96 and 97provide signals to the input and output sides of the detectortransformer 58 of the flow related channel. A seventh contact 98provides an input to the potentiometer 64.

in the operation of the illustrated embodiment of the circuit, thesystem is adjusted with a zero input signal to close the additivecontrol valve 6 and position the servo potentiometer 17 at zero. Theparts per million control potentiometer 64 is adjusted to introduce anadditive in a desired proportion to a preselected flow rate. Theenergization of the feedback potentiometer 17 is adjusted through thecalibration potentiometer 75, the span adjustment potentiometer 76 andthe pressure preset potentiometer 7%. Thus, the back pressure of theflow line is known and the voltage across the feedback potentiometer 17is adjusted to vary the control signal in accordance with the pressure.This will provide for direct modification of the opening of the linearflow additive valve 6 to maintain precise amounts of additive flowthrough the flow line 3 for the known back pressure of the line 1. Thecalibration potentiometer 75 and the span potentiometer 76 provide thenormal adjustment to the feedback potentiometer.

The linear additive valve 6 is then manually adjusted to establish theclosure with the servo system at zero condition.

When the flow is initiated, the turbine meter 7 will establish aproportionate signal which is converted into an alternating currentsignal and then detected by the transformer-rectifier network 54 57. TheDC. analog signal is amplified and applied across the parts per millionpotentiometer 64. The voltage at the tap 65 is amplified by theamplifier 67 and applied to the summing point via resistor 70. Thissignal is compared and summated with the output of the feedbackamplifier 72 to establish an error signal to the servo drive amplifier69 corresponding to the algebraic sum appearing at the summing inputpoint. The output is therefore either a positive or a negative voltagedepending upon the rela tive amplitudes of the two input signals. if theoutput of the flow related signal is greater than that of the feedbacksignal, a positive signal is assumed to be established and operates thepolarity sensitive relay 82 to close the forward contact 84 andcorrespondingly actuate the servomotor to drive the valve 6 in anopening direction. As the valve 6 opens, the tap 73 of the feedbackpotentiometer i7 is correspondingly changed to increase the input signalto the feedback amplifier 72 and thereby to the summing point until itssignal balances the signal of the flow related signal input. At thatpoint, the output of the servo amplifier 69 deenergizes the polaritysensitive relay 82 and the servomotor 16 stops and holds the linearvalve 6 in the desired flow position. If the flow rate increases, thusindicating that more material must be added to maintain the desiredproportionate rate of additive per unit of the main liquid, the inputsignal to the flow related amplifier 67 will increase, therebycorrespondingly establishing a positive input signal to the polaritysensitive relay 82. The relay 82 will again close the forward contact 84and provide power to drive the servomotor 16 to further open the valve6.

If, for any reason, the main liquid flow rate decreases, the signalapplied to potentiometer 64 decreases and the output of amplifier 67correspondingly decreases. As a result, the output of the feedbackamplifier 72 is relatively greater. The servo drive amplifier 69 willthen establish a relatively negative potential signal and actuates thepolarity sensitive relay 82 to drive the common pole 83 into engagementwith the valve closing or reverse contact 85. This energizes theservomotor 16 in the opposite direction resulting in a correspondingclosing of the valve 6 and a resetting of the feedback potentiometer 17.The valve 6 thus closes until the feedback potentiometer 17 provides arelated signal directly balancing the flow related signal therebyresulting in a deenergization of the polarity sensitive relay 82 andholding of the linear additive valve 6 in the proper flow position.

if, for any reason, the main flow decreases to a preselected minimum,the output signal of the amplifier 22 drops below the holding level ofthe main cutoff valve 2b. This, in turn, terminates the feeding ofadditive flow and may simultaneously operate an alarm or otherindication means, not shown.

Applicants have found that the differential amplifying and summingcircuit of this invention provides a rapid response and a reliabledriving of the valve to an accurate, additive tlow position where theproportion of the additive is a very small proportion of the total flow.Very small changes in the pulse rate from the turbine meter '7 israpidly and accurately sensed by the amplifier 67 and '72 feeding thesingle summing point, with an automatic and direct corrective drive ofthe linear metering valve 6 to establish and maintain a continuouscorrection in the injection rate of the additive and one which will,therefor, closely maintain the desired rate of additive proportional tothe variation in the flow rate of the main line. The servo circuit ofthe present invention thereby contributes to the provision of preciseinjection of the additive liquid within the main flow of a relativelyrapidly flowing liquid with a precise additive amount in the range ofparts per million on a continuous basis.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following laims, particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

We claim:

l. A metering additive control circuit for supplying relatively minutequantities of a liquid to a flowing liquid, comprising a linear meteringvalve connected to supply said additive liquid to said flowing liquid inaccordance with the opening of the valve, a reversible drive meansconnected to position said valve, a metering means establishing anelectrical signal proportional to the per unit volumetric flow throughthe metering means, selection means connected to said metering means andestablishing an additive rate si nal proportional to a selected rate ofadding said liquid, a differential summing amplifier including inputmeans connected to said selection means, a feedback signal means coupledand positioned by said drive means, said feedback signal means beingconnected to said input means, a polarity sensitive switching meansconnected to the output of said summing amplifier and having firstcircuit means and second circuit means actuated in response to acorresponding first and second polarity output of said summingamplifier, said drive means being connected to said first and secondcircuit means to correspondingly position said metering valve.

2. The metering additive control circuit of claim 1 including a linepressure compensating potentiometer having a tap for establishing asignal related to the pres ill sure in said flowing liquid, and meansconnecting the potentiometer to said input means.

3. The metering additive control circuit of claim 2 wherein said linepressure compensating potentiometer is connected in series with saidfeedback signal means.

4. The metering additive control circuit of claim 1 wherein saidselection means is a potentiometer connected to said metering means andhaving a selection output tap, said feedback means is a potentiometerhaving a feedback output tap coupled to said drive means, a firstamplifier connected to said selection output tap, a second amplifierconnected to said feedback output tap, a first linear summing resistorconnecting said first amplifier to the input means of said summingamplifier, and a second linear summing resistor connecting said secondamplifier to the input means of the summing amplifier.

5. The metering additive control circuit of claim 4 having a flowpressure compensating potentiometer connected in series with saidfeedback potentiometer to compensate for the pressure of the flowingliquid.

6. The metering additive control circuit of claim 1 wherein saidmetering means includes a pulse signal means to establish a pulse, trainsignal of corresponding amplitude pulses having a pulse rateproportional to the per unit volumetric flow through the meter, anamplifying means is connected to said signal means to convert saidpulses to an alternating current signal proportional to said pulse rate,a rectifying means is connected to said amplifying means and establishesa corresponding direct current signal, and said selection means includesa potentiometer connected to said amplifying means having an output tapconnected to said input means.

7. The metering additive control circuit of claim 6 wherein saidfeedback signal means includes a potentiometer having a feedback tapcoupled to said drive means, said feedback tap being connected to saidsumming input means, said polarity sensitive switching means being apolarity sensitive relay means connected to said summing amplifier andhaving first contact means in said first circuit means and closed inresponse to a first polarity and having second contact means in saidsecond circuit means and closed in response to a second polarity.

8. The metering additive control circuit of claim 1 wherein said meterincludes a pulse signal means to establish a pulse train signal ofcorresponding amplitude pulses having a pulse rate proportional to theper unit volumetric flow through the meter, a converting and amplifyingmeans connected to said meter and establishing an analog signalproportional to said pulse rate, said selection means including apotentiometer connected to said converting and amplifying means andhaving an output tap to select a proportionate part of said analogsignal, said feedback signal means including a potentiometer having afeedback tap coupled to said servomotor, said feedback tap beingconnected to said summing input means, said polarity sensitive switchingmeans including a polarity sensitive relay means connected to saidsumming amplifier and having first contact means closed in response to afirst polarity and second contact means closed in response to a secondpolarity, said drive means being a reversible servomotor having aforward drive circuit connected to said first contact means and areverse drive circuit connected to said second contact means.

9. In a metering additive control circuit for supplying relativelyminute quantities of a fluid material to a flowing liquid within a mainflow line by selectively positioning a valve opening in an additivesupply in accordance with a flow related signal and a valve positionfeedback signal, the improvement in a comparison and drive valve circuitcomprising a reversible servo-positioning drive motor coupled to saidvalve, a pulse signal means to establish a pulse train signal ofcorresponding amplitude pulses having a pulse rate proportional to theper unit volumetric flow through the flow line, a converting meansconnected to said meter and establishing an analog signal proportionalto said pulse rate, a potentiometer connected to said converting meansand having an output tap to select a proportionate part of said analogsignal, a summing amplifier including a summing input means connected tosaid potentiometer tap, a feedback signal potentiometer having afeedback tap coupled to said servomotor, said feedback tap beingconnected to said summing input means, a polarity sensitive meansconnected to said summing amplifier and having first means responsive toa first polarity drive signal to energize the servomotor in a firstdirection and second means responsive to a second polarity drive signalto energize said servomotor in a second direction.

1. A metering additive control circuit for supplying relatively minutequantities of a liquid to a flowing liquid, comprising a linear meteringvalve connected to supply said additive liquid to said flowing liquid inaccordance with the opening of the valve, a reversible drive meansconnected to position said valve, a metering means establishing anelectrical signal proportional to the per unit volumetric flow throughthe metering means, selection means connected to said metering means andestablishing an additive rate signal proportional to a selected rate ofadding said liquid, a differential summing amplifier including inputmeans connected to said selection means, a feedback signal means coupledand positioned by said drive means, said feedback signal means beingconnected to said input means, a polarity sensitive switching meansconnected to the output of said summing amplifier and having firstcircuit means and second circuit means actuated in response to acorresponding first and second polarity output of said summingamplifier, said drive means being connected to said first and secondcircuit means to correspondingly position said metering valve.
 2. Themetering additive control circuit of claim 1 including A line pressurecompensating potentiometer having a tap for establishing a signalrelated to the pressure in said flowing liquid, and means connecting thepotentiometer to said input means.
 3. The metering additive controlcircuit of claim 2 wherein said line pressure compensating potentiometeris connected in series with said feedback signal means.
 4. The meteringadditive control circuit of claim 1 wherein said selection means is apotentiometer connected to said metering means and having a selectionoutput tap, said feedback means is a potentiometer having a feedbackoutput tap coupled to said drive means, a first amplifier connected tosaid selection output tap, a second amplifier connected to said feedbackoutput tap, a first linear summing resistor connecting said firstamplifier to the input means of said summing amplifier, and a secondlinear summing resistor connecting said second amplifier to the inputmeans of the summing amplifier.
 5. The metering additive control circuitof claim 4 having a flow pressure compensating potentiometer connectedin series with said feedback potentiometer to compensate for thepressure of the flowing liquid.
 6. The metering additive control circuitof claim 1 wherein said metering means includes a pulse signal means toestablish a pulse train signal of corresponding amplitude pulses havinga pulse rate proportional to the per unit volumetric flow through themeter, an amplifying means is connected to said signal means to convertsaid pulses to an alternating current signal proportional to said pulserate, a rectifying means is connected to said amplifying means andestablishes a corresponding direct current signal, and said selectionmeans includes a potentiometer connected to said amplifying means havingan output tap connected to said input means.
 7. The metering additivecontrol circuit of claim 6 wherein said feedback signal means includes apotentiometer having a feedback tap coupled to said drive means, saidfeedback tap being connected to said summing input means, said polaritysensitive switching means being a polarity sensitive relay meansconnected to said summing amplifier and having first contact means insaid first circuit means and closed in response to a first polarity andhaving second contact means in said second circuit means and closed inresponse to a second polarity.
 8. The metering additive control circuitof claim 1 wherein said meter includes a pulse signal means to establisha pulse train signal of corresponding amplitude pulses having a pulserate proportional to the per unit volumetric flow through the meter, aconverting and amplifying means connected to said meter and establishingan analog signal proportional to said pulse rate, said selection meansincluding a potentiometer connected to said converting and amplifyingmeans and having an output tap to select a proportionate part of saidanalog signal, said feedback signal means including a potentiometerhaving a feedback tap coupled to said servomotor, said feedback tapbeing connected to said summing input means, said polarity sensitiveswitching means including a polarity sensitive relay means connected tosaid summing amplifier and having first contact means closed in responseto a first polarity and second contact means closed in response to asecond polarity, said drive means being a reversible servomotor having aforward drive circuit connected to said first contact means and areverse drive circuit connected to said second contact means.
 9. In ametering additive control circuit for supplying relatively minutequantities of a fluid material to a flowing liquid within a main flowline by selectively positioning a valve opening in an additive supply inaccordance with a flow related signal and a valve position feedbacksignal, the improvement in a comparison and drive valve circuitcomprising a reversible servo-positioning drive motor coupled to saidvalve, a pulse signal means to establish a pulse train signal ofcorresponding aMplitude pulses having a pulse rate proportional to theper unit volumetric flow through the flow line, a converting meansconnected to said meter and establishing an analog signal proportionalto said pulse rate, a potentiometer connected to said converting meansand having an output tap to select a proportionate part of said analogsignal, a summing amplifier including a summing input means connected tosaid potentiometer tap, a feedback signal potentiometer having afeedback tap coupled to said servomotor, said feedback tap beingconnected to said summing input means, a polarity sensitive meansconnected to said summing amplifier and having first means responsive toa first polarity drive signal to energize the servomotor in a firstdirection and second means responsive to a second polarity drive signalto energize said servomotor in a second direction.